The invention relates generally to phosphor compositions applicable to lighting systems. The invention also relates to lighting apparatus employing these phosphors and blends thereof.
Generation of “white light” is currently achieved by so called “white light emitting diodes (white LEDs)” that are constituted by employing a near-ultraviolet (UV) or blue emitting LED in conjunction with a phosphor or a blend of phosphors. Red-emitting phosphors based on complex fluoride materials activated by Mn4+, such as those described in U.S. Pat. No. 7,358,542, U.S. Pat. No. 7,497,973, and U.S. Pat. No. 7,648,649, absorb blue light strongly, and efficiently emit between about 610 nanometers and 635 nanometers with little deep red/NIR emission. Thus, the luminous efficacy and the quantum efficiency of white LEDs maximizes under blue excitation (440 nanometers-460 nanometers) as compared to other available red phosphors.
These complex fluorides can be utilized in combination with yellow-green emitting phosphors such as cerium-doped yttrium aluminum garnet Y3Al5O12:Ce3+ (YAG) or other garnet compositions to achieve warm white light (CCTs<5000 K on the blackbody locus, color rendering index (CRI)>80) from a blue LED, equivalent to that produced by current fluorescent, incandescent and halogen lamps. YAG has been mostly used in these white LED systems because of its broad emission spectrum that peaks in the yellow spectral region, and the high quantum efficiency of the LED system under blue light excitation. The drawback of YAG based LED systems is the relatively poor color rendering properties and high color temperature (CCT). For example, when an object is illuminated under such currently used white LEDs, they cannot imitate the colors illuminated by natural light.
Therefore, there is a need for phosphor compositions and blends that efficiently absorb blue radiation, provide high quantum efficiency, and result in improved color rendering in white light emitting lighting devices.